U.S. patent application number 10/597242 was filed with the patent office on 2008-09-25 for electrophoretic display device.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONIC, N.V.. Invention is credited to Neculai Ailenei, Mark Thomas Johnson, Guofu Zhou.
Application Number | 20080231592 10/597242 |
Document ID | / |
Family ID | 34802675 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080231592 |
Kind Code |
A1 |
Johnson; Mark Thomas ; et
al. |
September 25, 2008 |
Electrophoretic Display Device
Abstract
A display device (1) comprises electrophoretic particles (8,9)
and an image screen comprising an array of display elements
comprising a pixel electrode and a second electrode. The display
device comprises control means (15) for supplying drive signals to
the electrodes. In operation the image is displayed in subsequent
frames. The control means comprise a row driver (16) and a column
driver (10). Preset signals (53) are in operation supplied to the
display elements whereby the preset signals applied to display
elements alter between subsequent frames. The control means are
arranged to change preset-signals between frames in a
column-to-column scheme. The means for supplying preset signals are
arranged such that for the preset signals to at least a part of the
image screen comprising a group of columns and rows only one set of
data is transferred for the preset signals for said group.
Inventors: |
Johnson; Mark Thomas;
(Eindhoven, NL) ; Ailenei; Neculai; (Heerlen,
NL) ; Zhou; Guofu; (Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONIC,
N.V.
EINDHOVEN
NL
|
Family ID: |
34802675 |
Appl. No.: |
10/597242 |
Filed: |
January 12, 2005 |
PCT Filed: |
January 12, 2005 |
PCT NO: |
PCT/IB05/50132 |
371 Date: |
July 18, 2006 |
Current U.S.
Class: |
345/107 |
Current CPC
Class: |
G09G 2310/061 20130101;
G09G 2310/068 20130101; G09G 2310/0205 20130101; G09G 3/344
20130101; G09G 2300/08 20130101; G09G 2310/06 20130101; G09G
2310/0254 20130101; G09G 2320/0247 20130101 |
Class at
Publication: |
345/107 |
International
Class: |
G09G 3/34 20060101
G09G003/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 22, 2004 |
EP |
04100217.1 |
Claims
1. A display device (1) comprising electrophoretic particles (8,9),
an image screen comprising an array of display elements comprising
a pixel electrode and a second electrode between which a portion of
the electrophoretic particles are present, and control means (15)
for supplying drive signals to the electrodes to bring display
elements in a predetermined optical state corresponding to the
image information to be displayed, wherein in operation the image
is displayed in subsequent frames, said control means comprising a
row driver (16) and a column driver (10), and means for supplying
preset signals (53) to the display elements whereby the preset
signals applied to-display elements alter between subsequent
frames, wherein the control means are arranged to change preset
signals between frames in a column-to-column scheme and that the
means for supplying preset signals are arranged such that for the
preset signals to at least a part of the image screen comprising a
group of columns and rows only one set of data is transferred for
the preset signals for said group.
2. A display device as claimed in claim 1, wherein the group
comprises at least two columns.
3. A display device as claimed in claim 1, wherein display screen
is composed of n.times.m groups of columns and rows.
4. A display device as claimed in claim 2, wherein the display
screen is composed of two groups of columns and rows.
5. A display device as claimed in claim 1, wherein the group
comprises substantially all columns and rows-of the image
screen.
6. A display device as claimed in claim 3, wherein the display
screen is divided in quadrants, to each quadrant a group is
associated with its row and column driver.
7. A method for driving a display device (1) comprising
electrophoretic particles (8,9), an image screen comprising an
array of display elements comprising a pixel electrode and a second
electrode between which a portion of the electrophoretic particles
are present, and control means (15) for supplying drive signals to
the electrodes to bring display elements in a predetermined optical
state corresponding to the image information to be displayed,
wherein in operation the image is displayed in subsequent frames,
said control means comprising a row driver and a column driver, and
means for supplying preset signals (53) to the display elements
whereby the preset signals applied to display elements alter
between subsequent frames, wherein the control means are arranged
to change preset signals between frames in a column-to-column
scheme and that the means for supplying preset signals are arranged
such that for the preset signals to at least a part of the image
screen comprising a group of columns and rows only one set of data
is transferred for the preset signals for said group.
Description
[0001] The invention relates to a display device comprising
electrophoretic particles, an image screen comprising an array of
display elements comprising a pixel electrode and a second
electrode between which a portion of the electrophoretic particles
are present, and control means for supplying drive signals to the
electrodes to bring display elements in a predetermined optical
state corresponding to the image information to be displayed,
wherein in operation the image is displayed in subsequent frames,
said control means comprising a row driver and a column driver, and
means for supplying preset signals to the display elements whereby
the preset signals applied to display elements alter between
subsequent frames.
[0002] Display devices of this type are used in, for example,
monitors, laptop computers, personal digital assistants (PDA's),
mobile telephones, electronic books, electronic newspapers,
electronic magazines.
[0003] A display device of the type mentioned in the opening
paragraph is known from the international patent application WO
03/79324. This patent application discloses a electronic ink
display comprising two substrates, one of which is transparent, the
other substrate is provided with electrodes arranged in row and
columns. A crossing between a row and a column electrode is
associated with a display element. The display element is coupled
to the column electrode via a thin film transistor (TFT), the gate
of which is coupled to the row electrode. This arrangements of
display elements, TFT transistors and row and column electrode
together forms an active matrix. Furthermore, the display element
comprises a picture electrode, also known as a pixel electrode. A
select driver, generally referred to as a row driver, selects a row
of display elements and the data driver, generally referred to as a
column driver, supplies a data signal to the selected row of
display elements via the column electrodes and the TFT transistors.
The data signals correspond to graphic data to be displayed. The
image information, at least part of it, is updated and refreshed at
the transition from one frame to another.
[0004] An electronic ink is provided between the pixel electrode
and a common electrode provided on the transparent substrate. The
ink comprises positively charged white particles and negative
charge black particles suspended in a fluid. When a positive field
is applied to the picture electrode, the white particles move to
the side of the micro capsule directed to the transparent substrate
and the display element become visible to a viewer. Simultaneously,
the black particles move to the pixel electrode at the opposite
side of the microcapsule where they are hidden to the viewer. By
applying a negative field to the picture electrode, the black
particles move to the common electrode at the side of the micro
capsule directed to the transparent substrate and the display
element appears dark to a viewer. When the electric field is
removed the display device remains in the acquired state and
exhibit a bi-stable character.
[0005] Grey scales can be created in the display device by
controlling the amount of particles that move to counter electrode
at the top of the microcapsules. For example, the energy of the
positive or negative electric field, defined as the product of
field strength and time of application, controls the amount of
particles moving to the top of the microcapsules.
[0006] The optical response depends on the history of the display
element and a so-called underdrive effect is seen. This underdrive
effect occurs, for example, when an initial state of the display
device is black and the display is periodically switched between
the white and the black state. For example, after a dwell time of
several seconds, the display device is switched to white by
applying a negative field for an interval of 200 ms. In a
subsequent interval, no electric field is applied for 200 ms and
the display, remains white, and in a subsequent interval, a
positive field is applied for 200 ms and the display is switched to
black. The brightness of the display as a response of the first
pulse of the series is below the desired maximum brightness, which
can be reproduced several pulses later. In the prior art preset
signals are supplied, which preset signals comprise a pulse or a
series of pulses with an energy sufficient to release the
electrophoretic particle from a static state at one of the two
electrodes, but too low too reach the other one of the electrodes.
The preset signal reduces the underdrive effect. Because of the
reduced underdrive effect the optical response to an identical data
signal will be substantially equal, regardless of the history of
the display device and in particular its dwell time. The underlying
mechanism can be explained because after the display device is
switched to a predetermined state e.g. a black state, the
electrophoretic particles become in a static state, when a
subsequent switching is to the white state, a momentum of the
particles is low because their starting speed is close to zero.
This results in a long switching time. The application of the
preset pulses increases the momentum of the electrophoretic
particles and thus shortens the switching time. It is also possible
that after the display device is switched to a predetermined state
e.g. a black state, the electrophoretic particles are "frozen" by
the opposite ions surrounding the particle. When a subsequent
switching is to the white state, these opposite ions have to be
timely released, which requires additional time. The application of
the preset pulses (sometimes also called shaking pulses, since they
"shake up" the particles) speeds up the release of the opposite
ions thus the de-freezing of the electrophoretic particles and
therefore shortens the switching time. The application of the
preset pulses increases the momentum of the electrophoretic
particles and thus shortens the switching time.
[0007] A further advantage is that the application of the preset
pulses substantially eliminates a prior history of the electronic
ink, whereas in contrast conventional electronic ink display
devices requires massive signal processing circuits for the
generation of data pulses of a new frame, storage of several
previous frames and a large look-up table.
[0008] Such a preset pulse can have a duration of one order of
magnitude less than the time duration of an image update. An image
update is the instance where the image information of the display
device is renewed or refreshed.
[0009] Application of the preset signals, however, could also lead
to so called flicker. The preset signals do have a small effect on
the image displayed. In the prior art it is suggested to alter the
preset signals between frames. For example, when in a single frame
addressing period the preset pulses are applied with a positive
polarity to all even rows and a negative polarity to all odd rows
adjacent rows of the display device will appear alternately
brighter (e.g. the even rows) and darker (e.g. the odd rows) and in
the subsequent frame addressing period the positive and negative
polarities of the preset pulses are inverted, the odd rows will
appear brighter and the even rows will appear darker, as a
consequence the temporal perceptual appearance will then hardly be
effected, as the eye integrates these subsequent frames (temporal
averaging) so that odd and even rows appear to have substantially
equal brightness. A temporal smoothing of brightness deviations
occurs due to the fact that the preset signals are altered between
frames. This principle is similar to the line inversion principle
in methods for driving liquid crystal displays with reduced
flicker.
[0010] Thus by changing the preset signals between frames a
temporal averaging may be obtained which improves the image
rendition. The application of preset signals has, apart from a
positive effect, however also a negative effect, it requires energy
and time, and constitutes a restriction on the load and speed of
the drivers.
[0011] It is an object of the invention to reduce one or more of
the aforementioned problems.
[0012] To this end the display device in accordance with the
invention is characterized in that the control means are arranged
to change preset signals between frames in a column-to-column
scheme and that the means for supplying preset signals are arranged
such that for the preset signals to at least a part of the image
screen comprising a group of columns and rows only one set of data
is transferred for the preset signals for said group.
[0013] The preset signals require a data transfer to the drivers.
The inventors have realized that when a scheme is used in which
data for application of the preset signals is changed from row to
row (row inversion schemes) a vast amount of data is to be
transferred for each frame since each preset signal for each row
has to be separately addressed and requires transfer of preset
signal data. When a column inversion scheme is used, the inventors
have realized that it is possible to apply one set of preset
signals to the entire group without the need of changing the data
on the drivers. All rows in the group can be addressed with preset
signals, once a single set of data is provided to the data drivers
and it is not needed that the data drivers are provided with
further data. This strongly reduces the need for data transfer, the
energy and time required. It also offers a possibility to reduce
the total frame time, since the transfer of data, including data
for preset signals determines amongst others the frame time and
thereby the refresh frequency, i.e. number of frames per second.
The rows may be addressed one at a time, in the standard manner, or
alternatively more than one row could be addressed simultaneously,
for example by allowing a plurality of row drivers to run
simultaneously.
[0014] Preferably the group of columns and rows comprises
substantially all display elements.
[0015] Within the concept of the invention, the display screen may
be divided in a number of groups, for instance two groups, each
covering approximately half of the display screen, or 4 groups,
each covering a quarter of the screen, or n.times.m groups, each
covering a part of the screen. The groups may be intertwined. In
each embodiment the advantage is obtained. However, the smaller the
number of groups the larger the effect Preferred are therefore
embodiments in which there is only one group (i.e. the group covers
all display elements), or a small number of groups, 2, 4 or
n.times.m (where n,m=1,2,3). For large display devices (larger than
15'') it may be advantageous to divide the drivers and divide the
display screen in e.g. four quadrants, since this would reduce the
lengths of electrodes.
[0016] Further advantageous embodiments of the invention are
specified in the dependent claims.
[0017] In an embodiment the display elements are interconnected in
two or more groups whereby preset pulses having a different
polarity are supplied to the different parts of the screen. This
would reduce within a frame the spatial brightness
fluctuations.
[0018] Within the concept of the invention a `control means for
syppling` and "means for supplying" as well as in general "means
for" is to be broadly understood and to comprise e.g. any piece of
hard-ware (such a controller, supplier), any circuit or sub-circuit
designed for performing a control or a supply of one or more
signals as well as any piece of soft-ware (computer program or sub
program or set of computer programs, or program code(s)) designed
or programmed to perform such an act in accordance with the
invention as well as any combination of pieces of hardware and
software acting as such, alone-or in combination, without being
restricted to the below given exemplary embodiments.
[0019] The invention is also embodied in any computer program
comprising program code means for performing a method in accordance
with the invention when said program is run on a computer as well
as in any computer program product comprising program code means
stored on a computer readable medium for performing a method in
accordance with the invention when said program is run on a
computer.
[0020] These and other aspects of the invention are apparent from
and will be elucidated with reference to the embodiments described
hereinafter.
[0021] In the drawings:
[0022] FIG. 1 shows diagrammatically cross-section of a portion of
a display device,
[0023] FIG. 2 shows diagrammatically an equivalent circuit diagram
of a portion of a display device,
[0024] FIGS. 3 and 4 shows drive signals and internal signal of the
display device,
[0025] FIG. 5 shows an optical response of a data signal,
[0026] FIG. 6 shows an optical response of a preset signal and a
data signal
[0027] FIG. 7 shows preset signals for pixel electrode for two
adjacent rows consisting of 6 pulses of opposite polarities,
[0028] FIG. 8 illustrates a scheme in accordance with the
invention,
[0029] FIG. 9 illustrates a further scheme in accordance with the
invention
[0030] FIG. 10 illustrates yet a further scheme in accordance with
the invention.
[0031] The Figures are schematic and not drawn to scale, and, in
general, like reference numerals refer to like parts.
[0032] FIG. 1 diagrammatically shows a cross section of a portion
of an electrophoretic display device 1, for example of the size of
a few display elements, comprising a base substrate 2, an
electrophoretic film with an electronic ink which is present
between two transparent substrates 3,4 for example polyethylene,
one of the substrates 3 is provided with transparent picture
electrodes 5 and the other substrate 4 with a transparent counter
electrode 6. The electronic ink comprises multiple micro capsules
7, of about 10 to 50 microns. Each micro capsule 7 comprises
positively charged white particles 8 and negative charged black
particles 9 suspended in a fluid F. When a positive field is
applied to the picture electrode 5, the white particles 8 move to
the side of the micro capsule 7 directed to the counter electrode 6
and the display element become visible to a viewer. Simultaneously,
the black particles 9 move to the opposite side of the microcapsule
7 where they are hidden to the viewer. By applying a negative field
to the picture electrodes 5, the black particles 9 move to the side
of the micro capsule 7 directed to the counter electrode 6 and the
display element become dark to a viewer (not shown). When the
electric field is removed the particles 8, 9 remains in the
acquired state and the display exhibits a bi-stable character and
consumes substantially no power.
[0033] FIG. 2 shows diagrammatically an equivalent circuit of a
picture display device 1 comprising an electrophoretic film
laminated on a base substrate 2 provided with active switching
elements, a row driver 16 and a column driver 10. Preferably, a
counter electrode 6 is provided on the film comprising the
encapsulated electrophoretic ink, but could be alternatively
provided on a base substrate in the case of operation using
in-plane electric fields. The display device I is driven by active
switching elements, in this example thin film transistors 19. It
comprises a matrix of display elements at the area of crossing of
row or selection electrodes 17 and column or data electrodes 11.
The row driver 16 consecutively selects the row electrodes 17,
while a column driver 10 provides a data signal to the column
electrode 11. Preferably, a processor 15 firstly processes incoming
data 13 into the data signals. Mutual synchronisation between the
column driver 10 and the row driver 16 takes place via drive lines
12. Select signals from the row driver 16 select the pixel
electrodes 22 via the thin film transistors 19 whose gate
electrodes 20 are electrically connected to the row electrodes 17
and the source-electrodes 21 are electrically connected to the
column electrodes 11. A data signal present at the column electrode
11 is transferred to the pixel electrode 22 of the display element
coupled to the drain electrode via the TFT. In the embodiment, the
display device of FIG. 1 also comprises an additional capacitor 23
at the location at each display element 18. In this embodiment, the
additional capacitor 23 is connected to one or more storage
capacitor lines 24. Instead of TFT other switching elements can be
applied such as diodes, MIM's, etc.
[0034] FIGS. 3 and 4 show drive signals of a conventional display
device. At the instance t0, a row electrode 17 is energized by
means of a selection signal Vse1 (FIG. 1.), while simultaneously
data signals Vd are supplied to the column electrodes 11. After a
line selection time tL has elapsed, a subsequent row electrode 17
is selected at the instant t1, etc. After some time, for example, a
field time or frame time, usually 16.7 msec or 20 msec, said row
electrode 17 is energized again at instant t2 by means of a
selection signal Vse1, while simultaneously the data signals Vd are
presented to the column electrode 11, in case of an unchanged
picture. After a selection time tL has elapsed, the next row
electrode is selected at the instant t3. Because the bistable
character of the display device, the electrophoretic particles
remains in their selected state and the repetition of data signals
can be halted after several frame times when the desired grey level
is obtained. Usually, the image update time is several frames.
[0035] FIG. 5 shows a first signal 51 representing an optical
response of a display element of the display device of FIG. 2 to a
data signal 50 comprises pulses of alternating polarity after a
dwell period of several seconds. In FIG. 5 the optical response 51
is indicated by ---- and the data signal by ______. Each pulse 52
of the data signal 50 has a duration of 200 ms and a voltage of
alternating plus and minus 15 V. FIG. 5 shows that the optical
response 51 after the first negative pulse 52 is not a desired grey
level, which is obtained only after the third or fourth negative
pulse.
[0036] In order to improve the accuracy of the desired grey level
with the data signal the processor 15 generates a single preset
pulse or a series of preset pulses before the data pulses of a next
refresh field, where the pulse time is typically 5 to 10 times less
than the duration of an image update. In case the duration of an
image update is 200 ms, the duration of a preset pulse is typically
20 ms.
[0037] FIG. 6 shows the optical response to a data signal 60 of the
display device of FIG. 2 as a response to a series of 12 preset
pulses of short duration and data pulses of 200 ms having a voltage
of alternating polarity of plus and minus 15 V. In FIG. 6 the
optical response 51 is indicated by ----, the improved optical
response 61 by -.-.-.-.- and the data signal by ______. The series
of preset pulses consists of 12 pulses of alternating polarity. The
voltage of each pulse is plus or minus 15 V. FIG. 6 shows an
significant increase of the grey scale accuracy, the optical
response 61 is substantially at an equal level as the optical
response after the fourth data pulse 55. However, some flicker may
become visible introduced by the preset pulses, see optical
response 56. In order to reduce the visibility of this flicker, the
processor 15 and the row driver 16 can be arranged such that the
row electrodes 17 associated with display elements are
interconnected in two groups, and the processor 15 and the column
driver 10 are arranged for executing an inversion scheme by
generating a first preset signal having a first phase to the first
group of display elements and a second preset signal having a
second phase to the second group of display element, whereby the
second phase is opposite to the first phase. Alternatively,
multiple groups can be defined, whereto reset pulses are supplied
with different phases. For example, the row electrodes 17 can be
interconnected in two groups one of the even rows and one group of
the odd row whereby the processor generates a first preset signal
consisting of six preset pulses of alternating polarity of plus and
minus 15 V starting with a negative pulse to the display elements
of the even rows and a second preset signal consists of six preset
pulses of alternating polarity of plus and minus 15 V starting with
a positive pulse to display elements of the odd rows.
[0038] FIG. 7 shows two graphs indicative for an inversion scheme.
A first graph 71 relates to a first preset signal consisting of 6
preset pulses of 20 ms supplied to a display element of an even row
n and a second graph 72 related to a second preset signal
consisting of 6 preset pulses of 20 ms supplied to a display
element of an odd row n+1, whereby the phase of the second preset
signal is opposite the phase of the first preset signal. The
voltage of the pulse is alternating between plus and minus 15 V.
The first preset signal may be denoted by a plus sign (+), the
second by a minus sign (-).
[0039] Instead of the series of preset pulses applied to two or
more different groups of rows, the display elements can be divided
in two groups of columns, for example, one group of even columns
and one group of odd columns whereby the processor 15 executes an
inversion scheme by generating a first preset signal consisting of
six preset pulses of alternating polarity of plus and minus 15 V
starting with a negative pulse to the display elements of the even
columns and a second preset signal consists of six preset pulses of
alternating polarity of plus and minus 15 V starting with a
positive pulse to the display elements of the odd columns. The
above figures and explanation can also be found in the cited
document WO 03/79324. The spatial inversion scheme (i.e. providing
opposite signals to different groups e.g. odd and even rows)
provides for a reduction of spatial flicker. It is also remarked in
WO 03/79324 that a temporal inversion scheme may be used in which
in subsequent frames the polarity of the preset signals is
reversed. Such altering of the preset signals (polarity inversion)
leads to a temporal smoothing of brightness differences.
[0040] Whilst the above would result in the required flicker
reduction, it would require a high rate of data transfer (e.g. from
a memory/look-up-table) to the drivers, and a fast loading of the
drivers. These will result in an increase in power consumption. In
addition, the inventors have realized that there are systems
related problems if a shorter frame time is required. One of the
major limitations is the time required to load the data from the
memory/look-up-table onto the data drivers before it is driven onto
all the pixels of the row being addressed.
[0041] Transferring data usually requires several clock periods.
Even using parallel processing for a device having 800 columns and
600 rows, it was found that around 200 clock periods were required
to load all the data for the 800 columns onto the data drivers. As
the minimum clock period is 60 nsec, this results in at least a 12
microsecond line time. When a row inversion scheme of n rows (i.e.
inversion of signals within a frame is done in a row-to-row scheme)
is used it nominally requires n line periods to transfer all data,
making it impossible to reduce the frame time below 600
rows.times.12 microseconds=7.2 msec. With additional time required
for actually transferring the information, the shortest frame time
becomes around 8 msec.
[0042] In the invention a time-reduced flicker shaking is provided
by applying a column inversion approach. In a column inversion
approach the sign of the preset signals is the same along a column,
and is only altered between frames. The inventors have realized
that applying a column inversion scheme substantially shorter frame
times are possible, since they have realized that it is possible to
send information from the data drivers to the entire image (i.e.
all rows) to be shaken (i.e. to be provided with preset signals)
without changing the data voltages present on the drivers. For
example, during a shaking operation, the odd numbered rows of the
image may be addressed with a positive data voltage and the even
numbered rows of the image may be addressed with a negative data
voltage during one frame; whilst the even numbered rows of the
image may be addressed with a positive data voltage and the odd
numbered rows of the image may be addressed with a negative data
voltage during a following frame.
[0043] At the start of the first frame the data drivers are loaded
with the alternating positive/negative voltage data for the column
inversion for the first frame. This operation will require the
usual row time (12 microseconds in the above example) and could
precede the start of the frame if an entire image is being
addressed in this manner (for example in the blanking time between
2 frames). At this point, the first row is addressed. This
addressing period may now be shorter than the usual row time, and
will in practice only be limited by either the charging time of the
pixel through the addressing transistors, or by RC delay times
along rows or columns. Both of these limitations can be reduced by
technological choices (size of addressing TFT: pixel
capacitance/storage capacitance: resistance of row/column metals
etc) whereby an addressing time close to 1 microsecond could be
feasible. Subsequently, the remaining rows in the display are
addressed without the data drivers being provided with further
data. All subsequent rows receive the same data, whereby a column
inverted image is realized. In this case, all subsequent rows can
be addressed with the shorter addressing period (say 1
microsecond). In addition, no extra time will be required for
transferring data from the memories to the data drivers. In this
manner, a frame time of around 1 msec will be feasible.
[0044] Before the start of the following frame, data of the
opposite polarity is loaded into the data drivers in the usual
manner, and the rows of the new frame are addressed as above.
[0045] In this manner it is possible to reduce the frame rate to 5
msec or lower, and apply alternating shaking voltages to adjacent
columns in the display, and increase the flicker frequency to 100
Hz or higher, whereby the flicker would be removed.
[0046] In addition to the advantages of lower optical flicker, this
embodiment has the advantage of lower power as there is no data
transfer between memory/look-up-table and data drivers required
after first data loaded onto driver and in addition that the data
drivers do not need to continue clocking after first data is
loaded.
[0047] FIGS. 8 to 10 illustrate various embodiments of the
invention. In each figure a plus-sign stands for a preset signal of
any form and a minus-sign stands for the inverse preset signal. In
FIG. 8 all columns are given the same preset signal in frame A, and
the opposite signal in frame B. This will leads to a temporal
flicker reduction. In FIG. 9 a spatial inversion scheme is added.
In each frame, for adjacent columns the preset signals have
opposite signs. This provides for spatial flicker reduction. In
FIG. 10 in each frame n columns (in this example n=2, but may be
any number) receive preset signals of the same sign.
[0048] For large display devices it may be advantageous to provide
a plurality of the drivers and divide the display screen in e.g.
four quadrants. In this case, it would be possible to apply the
embodiments described above to only one or a to a subset of the
divided areas of the display, or to apply different embodiments to
different subsets of the divided areas. Diving the image screen
into quadrants is a most preferred embodiment. This reduces the
length of the electrodes very efficiently.
[0049] It is remarked that in the above example use is made of
inversion of the sign of the preset signal. Throughout the
specification the word "inversion" is often used. The invention is,
although simple inversion schemes are preferred embodiments due to
their simplicity, not restricted to such embodiments. The idea
behind the invention is that it is possible to use different preset
signals, wherein the preset signal is altered between frames, and
using a column-to-column scheme it is possible to do so by
transferring one, limited, set of data for each frame. In the
example the preset signals differ in sign, which is an easy way of
generating different signals. However, the preset signals may
differ in other aspects, for instance in length, in amplitude or in
number of sub-pulses.
[0050] It will be obvious that many variations are possible within
the scope of the invention without departing from the scope of the
appended claims.
[0051] The invention is also embodied in a method for driving a
display device (1) comprising electrophoretic particles (8,9), an
image screen comprising an array of display elements comprising a
pixel electrode and a second electrode between which a portion of
the electrophoretic particles are present, and control means (15)
for supplying drive signals to the electrodes to bring display
elements in a predetermined optical state corresponding to the
image information to be displayed, wherein in operation the image
is displayed in subsequent frames, said control means comprising a
row driver and a column driver, and means for supplying preset
signals (53) to the display elements whereby the preset signals
applied to display elements alter between subsequent frames,
wherein the control means are arranged to change preset signals
between frames in a column-to-column scheme and that the means for
supplying preset signals are arranged such that for the preset
signals to at least a part of the image screen comprising a group
of columns and rows only one set of data is transferred for the
preset signals for said group.
[0052] Furthermore the invention is embodied in a computer program
product comprising program code means stored on a computer readable
medium for use in a method in accordance with the invention when
said program is run on a computer.
[0053] It will be appreciated by persons skilled in the art that
the present invention is not limited by what has been particularly
shown and described hereinabove. The invention resides in each and
every novel characteristic feature and each and every combination
of characteristic features. Reference numerals in the claims do not
limit their protective scope. Use of the verb "to comprise" and its
conjugations does not exclude the presence of elements other than
those stated in the claims. Use of the article "a" or "an"
preceding an element does not exclude the presence of a plurality
of such elements.
[0054] The present invention has been described in terms of
specific embodiments, which are illustrative of the invention and
not to be construed as limiting. The invention may be implemented
in hardware, firmware or software, or in a combination of them.
Other embodiments are within the scope of the following claims.
* * * * *